how to place video inside of an image
You can use video or image sequence exactly the same way like texture.

In Node editor:
"Shift + A" -> "Texture" -> "Image sequence" (select all images "image.000" - "image.xxx"). 

Or you can choose "Texture" and open video file exactly like image.

Now you can setup video texture offset and start frame. 
Start frame: when video start playing (timeline frames)
Offset: set first frame where video start play (video texture frames) 

Example:
You need start playing video texture on frame 1250 of your animation and you want to jump on 10th second in your video texture. (remove first 10 second from video texture)

Set Start frame to 1250
Set offset to 240 (for 24FPS: 24 x 10 second)

There are also "Frames" - you can use it for stop play video texture. Frames = video texture frames, not your animation frames on timeline.

Second option is using Material ID for creating mask and add video to object using this mask in Video Sequence Editor or in Compositor. 

Personally I thing the 1st option is easiest way how to do it, just play with setup to achieve what you need. :-)